Construction machines such as hydraulic cranes, power shovels and the like generally have a Diesel engine mounted thereon as a power source for rotationally driving a hydraulic pump or pumps.
Heretofore, it has been the conventional practice to provide an engine control lever in the driver's cabin of a construction machine, connecting the engine control lever to an engine governor mechanism through a control cable, link rod or the like for engine control. However, such a control cable or link rod which mechanically connects the control lever to the governor mechanism involves a great deal of mechanical resistance which will require a large operating force in addition to a problem of low response characteristics.
In an attempt to improve these drawbacks, there has been proposed a system for electrically remote-controlling the engine governor mechanism (Japanese Laid-Open Utility Model Application 61-145849), the remote control system being provided with: a governor adjusting driving device including an electric motor and located in the vicinity of the engine; an adjustment sensor for detecting the extent of actually effected adjustment in terms of the rotational angle of the electric motor output shaft of the driving device; an operating device provided in the operator's cabin and adapted to produce a command signal commensurate with the extent of manipulation of an operation switch or other operating means; and a control device like a microcomputer adapted to control the rotation of the electric motor of the drive means on the basis of the detection signal from the adjustment sensor and the command signal from the operating device in such a manner as to zeroize the difference between the two signals.
With this arrangement, the control lever of the governor mechanism is turned to an extent corresponding to the extent of manipulation of the operating means through feedback control of the driving device, which zeroizes the difference between the above-mentioned detection and command signals.
However, the above-mentioned engine remote control system, which is arranged to turn the control lever of the governor mechanism into a tilted position by controlling the rotation of the electric motor of the driving device, needs to provide means for preventing impairment or breakage of the electric motor or control lever which might result from overrunning rotation of the electric motor.
Therefore, for the purpose of delimiting the rotational angle (operating range) of the electric motor, the prior art systems are usually provided with a couple of limit switches and a cam member on the output shaft of the electric motor.
Naturally, the system construction including such limit switches and a cam member requires an increased number of component parts, and accurate preadjustments of operating points of the respective component parts, which are very troublesome.
Further, for the feedback control of the electric motor, the prior art system is arranged to compare the command signal from the operating device with the detection signal from the adjustment sensor which detects the rotational angle of the electric motor, so that there arises a necessity for preadjustments to bring the output range of the command signals from the operating device into conformity with the detection range of the adjustment detector, making the operations for adjustments of actual variations extremely difficult.
The present invention contemplates to eliminate the above-mentioned drawbacks of the prior art system, and has as its object the provision of an engine remote control system which is adapted to actuate and deactuate a driving device in relation with variations in the degree of tilting of the governor mechanism which is checked up in each program cycle, obviating the use of limit switches and a cam which have been conventionally resorted to for detection of the limits of the rotational angle of the driving device and unnecessitating the interrelating preadjustments of the operating and detecting devices.